Soot Modeling for Advanced Control of Diesel Engine Aftertreatment

Diesel particulate filters (DPFs) are well assessed aftertreatment devices, equipping almost every modern diesel engine on the market to comply with today’s stringent emission standards. However, an accurate estimation of soot loading, which is instrumental to ensuring optimal performance of the whole engine-after-treatment assembly, is still a major challenge. In fact, several highly coupled physical-chemical phenomena occur at the same time, and a vast number of engine and exhaust dependent parameters make this task even more daunting. This challenge may be solved with models characterized by different degrees of detail (0-D to 3-D) depending on the specific application. However, the use of real-time, but accurate enough models, may be the primary hurdle that has to be overcome when confronted with advanced exhaust emissions control challenges, such as the integration of the DPF with the engine or other critical aftertreatment components (selective catalytic reduction or other NO_x control components), or to properly develop model-based OBD sensors. This paper aims at addressing real time DPF modeling issues with special regard to key parameter settings, by using the 1-D code called ExhAUST (exhaust aftertreatment unified simulation tool), which was jointly developed by the University of Rome Tor Vergata and West Virginia University. ExhAUST is characterized by a novel and unique full analytical treatment of the wall that allows a highly detailed representation of the soot loading evolution inside the DPF porous matrix. Numerical results are compared with experimental data gathered at West Virginia University engine laboratory using a MY2004 Mack^®MP7-355E, an 11 liter, 6-cylinder, inline heavy-duty diesel engine coupled to a Johnson Matthey CCRT diesel oxidation catalyst + CDPF, catalyzed DPF exhaust aftertreatment system. To that aim, the engine test bench was equipped with a DPF weighing system to track soot loading over a specifically developed engine operating procedure. Results indicate that the model is accurate enough to capture soot loading and back pressure histories with regard to different steady state engine operating points, without a need for any tuning procedure of the key parameters. Thus, the use of ExhAUST for application to advanced after-treatment control appears to be a promising tool at this stage.